The present invention is concerned with a method for the adaptive control of the hydraulic pump of a controlled brake system containing low-pressure accumulators which take up at least a part of the pressure fluid discharged, in case of control, from the wheel brakes and which are evacuated by the hydraulic pump. In this method, a volume model is formed by sensing and evaluating of parameters determining the pressure fluid flow, which volume model approximately indicates the discharge and supply of pressure fluid.
DE 38 18 260 A1 discloses a circuit configuration for controlling the auxiliary energy supply of a brake system provided with anti-locking control and/or traction slip control systems, whereinxe2x80x94by measuring and evaluating parameters determining the required auxiliary energy or the pressure fluid flowxe2x80x94a volume model is formed which approximately indicates the pressure fluid discharge from the master cylinder of the brake system and the pressure fluid requirement. The said volume model is used for controlling the auxiliary energy supply, namely for actuating and de-actuating a hydraulic pump, thereby insuring a low auxiliary energy consumption, relatively low pressure fluctuation amplitudes during a control process and an improved pedal comfort because the undesired set-back of the brake pedal during activation of the pump is reduced.
In another conventional brake system described in DE 42 32 614 A1 the filling level of the low pressure accumulator of a hydraulic brake system provided with an anti-locking control system is determined by measuring and evaluating the pressure at the inlet of the low pressure accumulator or with the aid of a way-sensor measuring the stroke of the piston in the low pressure accumulator, and evaluated for determining the required delivery capacity of the pump, and, finally, for controlling the hydraulic pump.
Moreover, D 44 40 517 A1 teaches a method for controlling the return pump of a brake system in which the pump is controlled in response to the value of a variable and/or a control deviation of a controller affecting the brake moment or the number of revolutions of the wheel.
Finally, EP 05 77 609 B1 teaches to reduce, in a brake system comprising an anti-locking control and a traction slip control system (ABS and ASR), the number of revolutions of the hydraulic pump in the ASR-mode by limiting the power input of the electric motor actuating the pump to reduce the development of noise. In safety-critical situations or in special cases of malfunction the input limitation becomes abandoned.
Now, it is the object of the invention to provide a method for determining the actually required delivery capacity and, hence, for determining, with relative accuracy, the number of revolution momentarily required. It is intended to determine the lowest possible yet in any case adequate number of revolutions which also in critical situations and in unfavorable circumstances is still sufficient.
For safety reasons, a speed and delivery capacity adequate in all eventualities has been mandatory. Conversely, a high value has been attached to a low number of revolutions of the pump to avoid the development of disturbing noises dependent on the number of revolutions, and to enhance the pedal comfort affected by undesired pedal movements.
It has been found that this problem, in the practice of the invention, can be solved by a method, the special features of which reside in that, in a first step, the course of the brake pressure at least approximately is determined for each individual wheel; that on the basis of the course of the brake pressure within the wheel brakes connected to a brake circuit, a volume model is formed for each brake circuit which approximately indicates the pressure fluid volume taken up by each low-pressure accumulator, and the filling level of the low-pressure accumulator, respectively; that the control frequency and the time interval between two successive brake pressure decreasing phases, respectively, are determined; and that the delivery capacity of the hydraulic pump is so dimensioned that the time interval between two successive phases will (just) be adequate for completely evacuating the low-pressure accumulator.
The method of the invention, hence, is based on a numerical evaluation of the data available. The provision of additional sensors is foregone. First, the wheel brake pressure is determined for eachxe2x80x94individualxe2x80x94wheel, preferably by a so-called wheel pressure model; then the volume model indicating the filling level (or the available residual volume of the accumulator) from the actuating time of the outlet valve and the wheel pressure of the connected wheel brakes is determined for eachxe2x80x94individualxe2x80x94brake circuit. According to a preferred form of embodiment, the maximum value of the filling level determined in the form of the volume model is selected and, based thereon and on the control frequency or on the time interval between two successive brake pressure decreasing phases, the number of revolutions of the pump is dimensioned.
The invention is based on the recognition that the number of revolutions of the pump adequate for immediately and completely evacuating the low-pressure accumulator and axe2x80x94apart from a certain safety marginxe2x80x94by no means higher than absolutely required, can be determined in the afore-described way, thereby safeguarding the brake functions and at the same time minimizing the development of noise.
According to another preferred form of embodiment of the invention a wheel brake pressure model based on the momentary deceleration of the automotive vehicle which is a measure of the momentary blocking pressure level, is numerically formed on the basis of the valve actuating times and the pressure/volume characteristic of the system for determining the course of the brake pressure within the individual wheel brake for each individual wheel. Theoretically, it would also be possible to use for each wheel a pressure sensor, which, however, would involve substantially enhances costs.
The volume model indicating the filling level of the low pressure accumulator (or the available residual volume), in the practice of the invention, is based on the course of the brake pressure determined for each individual wheel, on the outlet valve actuating times and, of course, on the pressure-volume characteristic of the hydraulic system. It is also in this respect that the provision of sensors has been foregone.
Moreover, it has proved advantageous to fix in response to the volume model and to the maximum filling level in the low pressure accumulators evacuated by a common hydraulic pump, a minimum value or a pre-controlled value of the number of revolutions of the pump, which is then compared to the number of revolutions of the pump determined in response to the control frequency. This is a safety measure for insuring a minimum number of revolutions. The minimum value will take effect only if the number of revolutions responsive to the control frequency is lower.
The afore-mentioned minimum value or the pre-controlled value is dependent on the momentary filling level of the low pressure accumulator, namely on the maximum value. Moreover, it is possible to vary the minimum value in response to the speed of the automotive vehicle. At low speeds, a relatively low number of revolutions certainly will in any case be adequate.
Further features, advantages and fields of end-use application of the invention will become manifest from the following description of additional details of the invention with reference to the accompanying drawings.